most important mechanic against kat is a way to either escape or interrupt her utli. Swain, annie, kass, diana are all good, she is also very weak against some ad mids such as sion or pantheon. in lane pre 6 she its possible to harass her out and out cs/lvl her. she has to either use spells or be in melee range to last hit, just remember she has no mana issues so don't force yourself oom trying to harass her because this will quickly lose you the lane. once your out of lanening as long as you have someone on your team saving something to interrupt her ult you can negate most of her damage in team fights.